This invention relates to a novel composition of luminescent paint useful for example, in lighting interior spaces, material surfaces and objects. The luminescent paint may be exposed to light, either natural or artificial, for a specific minimum amount of time, before giving off light for a specific and measurable amount of time and level of luminosity. The base color of the luminescent paint can be tinted with readily available paint tints in certain range of light colors. The luminescent paint has about the quality and characteristics of standard paint with respect to applicability, appearance (orange peel), durability, and method of use.
This tintable luminescent paint has interior applications whereby the painted surface can act as a wayxe2x80x94finding devise in a scenario where no other light is available. Specific application methods can provide sufficient light, comparable to emergency lighting devises, in corridors, exist stairs, etc.
Luminous products have been manufactured for many years although most products have been in an extruded plastic form or from coating the product in a manufacturing environment. Originally luminous products were more intended as a trinket, toy or novelty item.
As phosphorescent phosphors, sulfide phosphorescent phosphors are known Examples of sulfide phosphorescent phosphors include CaS:Bi (which emits light of violet blue), CaStS:Bi (which emits light of blue), ZnS:Cu (which emits light of green) and ZnCdS:Cu (which emits light or yellow or orange). However, any of these sulfide phosphorescent phosphors is chemically unstable and can suffer from degraded light resistance.
Another known type of phosphor is available under the trademark LUMINOVA (described in U.S. Pat. No. 5,424,006). This type of phosphor is an alkali earth (strontium, barium, calcium) oxide aluminate, and can also include rare earth elements. It has the advantage of being relatively bright in color, and shows excellent phosphorescence. It has the serious disadvantages of being sensitive to moisture, and being relatively dense and so difficult to mix.
U.S. Pat. No. 5,874,491 relates to phosphorescent highway paint incorporating this type of phosphor. The inventor found that the mixing of the phosphor in a water soluble polyurethane, or an epoxy, paint composition, provided a relatively stable composition useful in marking road surfaces. The mixture of the luminescent substance with a water-soluble polyurethane or epoxy resin agglomerates or encapsulates the pigment. These could be mixed with water-based highway paints. Unfortunately, such resins are expensive and unsuitable for applications where it is desired to have a normal-looking, durable and cost effective painted surface. Encapsulation of the phosphor also increases the effective particle size of the phosphor, and makes it difficult to incorporate a substantial amount of the phosphor into a paint thereby reducing the amount it can glow, in addition to the typical characteristics of the product, and making it difficult to use. The paint disclosed would not be suitable for interior walls, and would not apply as easily as normal paint.
The product of this invention is durable enough to be used on exterior surfaces, but tests on this and other formulations (such as U.S. Pat. Nos. 6,005,024 and 5,874,491 by Anders) show that exterior applications are not effective because of the natural dimming of sunlight and other ambient light which in most cases in unpreventable. The first, natural dimming of sunlight affects the applied surface in a number of ways. The surface will absorb the UV radiation and will glow but it will glow as the sun goes down and sunlight dims. Unless the product is very heavily pigmented the glow will have diminished before complete darkness occurs. In addition, if any transitory ambient or direct light (like headlights) shone on the luminescent surface, it will be undistinguishable from the area around it, thereby discounting the product""s luminescent quality.
Our tests have show the Luminova(trademark) pigment adds yellow coloration to any formula in which it is used at a ratio of higher than 5%. The clear type products such as the epoxy system for road ways/highways, airport runways, traffic control surface markings described in U.S. Pat. No. 6,005,024 would be difficult to produce as a clear overlay at that ratio. In addition the two step epoxy system is limiting because of its application (i.e. it must be completely used immediately after mixing the two components). Luminescent epoxy products have been available for many years.
Water based compositions have been devised using a zinc sulfide pigment, although it is limiting in its application as it must be used after opening because the luminescent particles may lose their ability to glow if left unattended.
Alternative emergency way-finding devises are increasingly more important and are described in U.S. Pat. Nos. 5,904,017 and 4,522,861, where accessories or attachments can provide luminosity to emergency escape paths and stair treads. These accessories are generally very awkward to install, unpleasant from a design perspective and require special tools or machinery to install.
Prior patents (Anders"" U.S. Pat. No. 5,874,491) claim that their product can be produced in various colors including white (using titanium dioxide), yellow (chrome yellow), orange, blue and green It has been our experience that the addition of great amounts of pigments masks the luminosity levels as the additional particle covers the luminescent particles. The luminescent pigment, such as LUMINOVA(trademark) pigment has a natural yellow colour that does not change greatly with the addition of titanium dioxide. If the pigment is dark it absorbs the light and produces less of a glow. Our formulation has a base tone that can be tinted with a specific range of light tints as per the process which regular paint is pigmented.
I have found that by combining LUMINOVA phosphors with an alkyd base, a rheology improver, another pigment, an anti-skin additive, and other ingredients, I can achieve a luminescent paint that has characteristics including tintability, applicability, viscosity, appearance and coloration comparable to a non-luminescent paint, with adequate protection from moisture and at a relatively reasonable cost.
An alkyd base formulation is the preferred formulation that will allow for the highest amount of loading without compromising the quality of the paint with respect to appearance or applicability. The appearance of the paint in daylight has minimal orange peel or pockmark affects because of the ability for this formulation to suspend and diffuse the large luminescent particles effectively while applying the product. In many other products unattractive daylight appearance is a limiting factors. In addition because of the effectiveness of this formulation the appearance of the glow is even, consistent and undisrupted in a properly installed scenario. This product is non abrasive and will provide a smooth, even appearance.